The present invention relates to a range measuring method, a range measuring apparatus, a non-contacted IC medium and a range measuring system, which measures a range, for example, from a reader unit to a non-contacted IC medium.
There is a range measuring apparatus that measures the range to a non-contacted IC medium using multiple frequencies (refer to International Publication WO 2006/095463). The range measuring apparatus controls an RFID tag (non-contacted IC medium) to transmit two times a R/W request signal that requests transmission of a tag response signal. At this time, a frequency controller controls a PLL portion to transmit respective R/W request signals by transfer frequencies differing from each other. A phase information acquisition portion detects fluctuation amounts in phase of tag response signals transmitted by the transfer frequencies differing from each other, respectively, and calculates the range between a reader/writer and the RFID tag based on the fluctuation amounts in the phase. Therefore, the range between the reader/writer and the RFID tag can be accurately calculated.
However, it cannot be necessarily said that the non-contacted IC medium always stops at a fixed position. And, there is a case where the range to a non-contacted IC medium in motion is requested to be obtained. In such a case, since the above-described range measuring apparatus carries out transmission and receiving of different frequencies at different timings, a deviation occurs at the receiving timing. Therefore, where the non-contacted IC medium is conveyed at a high speed, it is difficult to accurately calculate the range.